There are probably greater ones than these listed but we may never know due to the fog of war.
1. 9343 dead, Wilhelm Gustloff torpedoed in Baltic Sea, 30th Jan 1945.
2. 6200 dead, Goya torpedoed in Baltic, 16th Apr 1945.
3. 5620 dead, Junyo Maru torpedoed off Sumatra, 18th Sep 1944...